1. Field of the Invention
The present invention relates generally to a plasma treatment system and method for depositing a thin film, such as SiOF and SiO.sub.2 films, on a substrate to be treated, such as a semiconductor wafer, by a plasma treatment, such as an ECR (Electron Cyclotron Resonance) treatment.
2. Related Background Art
An aluminum wiring is typically used as a wiring pattern for an integrated circuit. An SiO.sub.2 film, an SiOF film or the like is typically used as an interlayer insulator film for insulating the aluminum wiring. These films are formed by means of, e.g., a plasma treatment system for carrying out the ECR plasma treatment as shown in FIG. 11.
For example, in this system, a microwave of, e.g., 2.45 GHZ, is supplied to a plasma producing chamber 1A by means of a waveguide 11, and a magnetic field of, e.g., 875 gausses, is applied thereto, so that the interaction (the Electron Cyclotron Resonance) between the microwave and the magnetic field activates a plasma gas, such as Ar or O.sub.2 gas, and a thin film deposition gas, such as SiH.sub.4 gas, which is introduced into a thin film deposition chamber 1B, to produce plasma serving as active species to deposit a thin film on a semiconductor wafer (which will be hereinafter referred to as a "wafer") W mounted on a mounting table 12.
The magnetic field is applied as a downward magnetic field, which extends from the plasma chamber 1B to the thin film deposition chamber 1B, by the combination of a main electromagnetic coil 13, which is provided so as to surround the plasma chamber 1A, and an auxiliary electromagnetic coil 14, which is provided below the thin film deposition chamber 1B.
By the way, the above described plasma treatment system is designed to adjust the shape of the magnetic field by changing the currents flowing through the main electromagnetic coil 13 and the auxiliary electromagnetic coil 14 since the main electromagnetic coil 13 and the auxiliary electromagnetic coil 14 are fixed to the aforementioned positions. However, in a case where only such adjustment of coil current is carried out, when only the current of one of the electromagnetic coils is adjusted, the shape of the magnetic field itself is not changed although the intensity of the magnetic force on the magnetic potential surface of the magnetic field applied by the adjusted electromagnetic coil is changed.
For example, a divergent field shown in FIG. 12 can be obtained by causing the current flowing through the auxiliary electromagnetic coil 14 to be far smaller than the current flowing through the main electromagnetic coil 13 or to be zero. However, if only the current flowing through the main electromagnetic coil 13 is increased without changing the current flowing through the auxiliary electromagnetic coil 14, only the intensity of the magnetic force on the magnetic potential surface shown by the dotted lines in FIG. 12 is increased.
In addition, when the respective currents of the main electromagnetic coil 13 and the auxiliary electromagnetic coil 14 are adjusted, the shape of the magnetic field is greatly changed. For example, when the current flowing through the auxiliary electromagnetic coil 14 is higher than that in the case of the divergent field, a mirror field shown in FIG. 13(a) is formed, and when the direction of the current flowing through the auxiliary electromagnetic coil 14 is inverted, a cusp field shown in FIG. 13(b) is formed. As described above, the shape of the applied magnetic field changed by only the adjustment of currents flowing through the electromagnetic coils is restricted, and the degree of freedom for the shape of the obtained magnetic field is small.
By the way, in recent years, a thin film of a two-layer structure obtained by stacking an SiOF film and an SiO.sub.2 film is provided in order to obtain a high quality interlayer insulator film. Such a film is continuously formed in, e.g., the above described plasma treatment system. However, the conditions in the processes for depositing these films are different from each other. If the shape of the magnetic field is optimized for one of the films, the inplane uniformity of thickness of the other film is deteriorated.
Therefore, it is required to adjust the shape of the magnetic field so as to enhance the inplane uniformity of thickness of both films. However, as described above, the degree of freedom for the shape of the magnetic field is small in the present circumstances, so that it is very difficult to adjust the shape of the magnetic field. In recent years, the scale down of devices is accelerated, so that it is required to provide thinner interlayer insulator films. Therefore, it is conceived that it is more difficult to adjust the shape of the magnetic field.